1. Field of the Invention
This invention relates to a process for incorporating a plasticizer into a polyamide in the solid phase, under mild conditions without melt processing.
2. Discussion of the Background
Polyamides are generally rigid materials. For numerous applications, for example shoe soles, fuel and compressed air brake lines or cable casings, they must be rendered flexible by addition of plasticizers.
Plasticizers are usually incorporated into polymers starting with a physical blend of polyamide granules or pellets and plasticizer mixture. This mixture is typically melted and homogenized in a kneader or extruder. The melt is then forced through a perforated plate or die, and the polymer strands are cooled in water and chopped into pellets. However, this process is expensive since it requires special kneaders or mixers with corresponding metering devices to incorporate the correct percentage of plasticizer. In general it takes at least two pelletizing and two drying steps to produce plasticized polymer from monomer.
It is also known, from DE-A 21 53 249, corresponding to U.S. Pat. No. 3,846,357, to blend plasticizers into the polymerized polyamide melt in the reactor. The disadvantage with this process is the heat-sensitive plasticizers decompose during the typical 5- to 8-hour residence time in the reactor at the required temperature range of 220.degree. to 260.degree. C. Plasticizers subsequently undergo undesirable side reactions which damages the product. Deterioration in color is also observed. In this procedure, furthermore, the plasticizer is often partly emitted in the form of an aerosol during discharge of the melt from the reactor. Health problems may arise in the workplaces from such emissions.
DE-A 36 13 528 describes another form of plasticizer incorporation, in the presence of a polyalkenamer. Liquid auxiliaries and additives are incorporated at a temperature of not more than 70.degree. C. However, the process described therein cannot be applied to polyalkenamer-free polymers.